1. Field of the Invention
This invention relates to a display device having a display element capable of assuming visually different states, and a plurality of which can be arranged to display a letter, a numeral etc., by selectively positioning each of the display elements in one of above-mentioned different states selectively, and more particularly pertains to such a device in which the display element has visually-different surface portions and is rotated to display one of such portions.
2. Description of the Prior Art
Hitherto known display devices for displaying a numeral, a letter, etc., for a large digital clock, score indications at gymnasia, road information indications, etc., are known.
One example of such a prior art device is as shown in FIGS. 1 and 2. In this figure, numeral 1 represents an axis and a display element 2 in the form of a spherical body is rotatably supported on the axis 1 in the plane of a panel 8. The surface of the display element 2 has a black colored portion 3 and a yellow colored (containing a luminous paint) portion 4, each portion extending over about 180.degree. of the circumferential surface of the body 2. A permanent magnet 5 is provided within the display element 2. Adjacent to the display element 2 is an electromagnet 6 with one end of its core 7 facing the permanent magnet 5. By selectively polarizing the electromagnet 6, the desired surface i.e. either the black colored portion 3 or the yellow colored portion 4 can be displayed by creating a repelling or attracting force between the electromagnet 6 and the permanent magnet 5. By arranging a plurality of such units in a matrix, as shown in FIG. 2, and displaying the yellow colored portion 3 of suitable units a desired numeral or letter can be displayed. In the daytime, contrast of the display with the panel is obtained by reflection of sunlight, but at night the display elements 2 are irradiated with ultraviolet rays from a black light, so that luminous paint coated on the yellow colored portion 4 emits luminescence to give contrast to the display.
The display by such luminescence, however, lacks clearness. In practice sufficient doses of black light are not delivered from the black light to the display elements when the arrangement is located far from the black light, resulting in extremely poor brightness. Therefore brightness is not uniform over the whole area of the arrangement so that visibility is not good.
Furthermore the luminous paint deteriorates with the passage of time, decreasing brightness. Especially in use outdoors the deterioration is so severe that the service life of the display element 2 is short.
Further because the luminous paints are available only in a small number of color types, the display color is limited.
Another example of a prior art display device is one in which a plurality of electric bulbs or fluorescent lamps are arranged in a matrix or in a figure " ", and the display of a numeral or a letter is made by turning on the electric bulbs or the fluorescent lamps at specified positions.
Such a display device, however, has drawbacks as follows:
1. It is hard to be seen when exposed to direct sunlight.
2. Since the electric bulbs or the fluorescent lamps need to be always energized when the indication is continuously made, the amount of power consumed is large.
3. Since many bulbs or fluorescent lamps are used, maintenance of the device including their replacement because of breakage is costly.